Earth-Sized Planet With One-Year Orbit Could Be Our Best Chance To Find Life

A Frozen Twin Hidden in Plain Sight

Astronomers have discovered what might be Earth's icy cousin lurking in data from NASA's retired Kepler Space Telescope. The planet, called HD 137010 b, is almost exactly Earth-size. At 355 days, its orbit is almost exactly Earth-like, too. And its star is bright and just 146 light-years away–close enough to be observed in detail with future telescopes. What makes this discovery particularly remarkable is that the faint event had gone unnoticed for years because automated searches expected repeating signals, leaving this lone crossing hidden in plain sight.

HD 137010 b was first flagged as a potential planet candidate by citizen scientists participating in the Planet Hunters project, which sifts through data from NASA's Kepler Space Telescope. A brief 10-hour dip in the star's light first revealed the presence of the world now called HD 137010 b. Analyzing that signal, Alexander Venner of the Max Planck Institute for Astronomy (MPIA) showed that the dimming matches the passage of a planet only slightly larger than Earth.

The discovery represents a breakthrough in the search for potentially habitable worlds. Overall, astronomers have discovered more than 6000 exoplanets. But the overwhelming majority are big, hot, or both, because such worlds are easiest to detect. Among the several dozen known habitable-zone, roughly Earth-size exoplanets, most are found in tight orbits around M-dwarf stars.

A Cold World at the Edge of Possibility

Despite its Earth-like dimensions, HD 137010 b faces a significant challenge: extreme cold. HD 137010 b's star is a K-dwarf, relatively bright but about 1000°C cooler than the Sun. So despite orbiting at about the same distance as Earth, the planet receives less energy from its star than Mars. That could mean a planetary surface temperature no higher than minus 90 degrees Fahrenheit (minus 68 degrees Celsius). By comparison, the average surface temperature on Mars runs about minus 85 degrees Fahrenheit (minus 65 degrees Celsius).

However, the planet's position isn't entirely hopeless. That would put it right at the icy edge of the star's habitable zone, a region around a star within which planets get enough sunshine for water to potentially be liquid on their surfaces. The team calculated about a 40% chance that it orbits its star more closely, firmly within the habitable zone. Climate models suggest that a moderately CO2-rich atmosphere would be conducive to liquid surface water.

The Challenge of Confirmation

The biggest hurdle facing HD 137010 b is confirmation. With only a single transit recorded so far, the system now stands as a compelling candidate that still requires another observation to confirm the planet's orbit. That job is difficult because a yearlong orbit gives astronomers few chances, and each predicted window still carries uncertainty.

HD 137010 b could have a year lasting anywhere from about 300 to 550 days, the authors say. That huge range not only complicates the search for more transits; it also means this notional near twin of Earth could be so far from its slightly dimmer star that it would instead be more like a frozen, supersized version of Mars. Confirmation seems unlikely, for now. No other exoplanet-hunting telescope currently plans to even look at the star, let alone scrutinize it long enough to bag more transits.

A New Era of Discovery

What sets HD 137010 b apart from previous discoveries is its accessibility for future study. HD 137010 b stood out because it combined small size, a long orbit, and a host star bright enough for serious follow-up. Because the host star is bright, future instruments can gather cleaner light and ask sharper questions about the system. This advantage could prove crucial as astronomers develop more sophisticated methods to analyze distant worlds.

The discovery demonstrates that Earth-like planets may be more common than previously thought, even if they remain challenging to detect. The discovery of HD-137010 b "demonstrates the detectability of temperate and cool Earth-sized exoplanets orbiting Sun-like stars through single transits," the researchers explain. As technology advances and new space telescopes come online, HD 137010 b could become the first confirmed Earth-like planet around a Sun-like star that's close enough for detailed atmospheric analysis—potentially answering whether we're alone in the universe.